1. Field of the Invention
The present invention relates to a hard coat film. More particularly, the present invention relates to a hard coat film used for surface protection of touch panels of the resistance film type and optical disks.
2. Description of Related Art
Hard coat films have heretofore been used for protection of surfaces in various image display apparatuses such as LCD (liquid crystal displays), touch panels, CRT (cathode ray tubes), PDP (plasma display panels), EL (electroluminescence displays) and optical disks.
Touch panels are used as the input apparatus for portable information terminals which are being widely used in recent years. The touch panel is an apparatus for inputting data by directly touching the surface of a display by a finger or a pen. About 90 percent of the entire touch panels are the touch panels of the resistance film type. The touch panel of the resistance film type has, in general, a structure in which a plastic substrate of the touching side which has a transparent electrically conductive (referred to as “conductive”, hereinafter) thin film such as a film of indium oxide doped with tin (ITO) laminated on one face of a transparent plastic substrate and a transparent substrate of the display side which has a transparent conductive thin film such as an ITO film laminated on one face of a transparent substrate material such as a glass plate are arranged with an insulating spacer placed between the two substrates in a manner such that the transparent conductive thin films in the two substrates are faced to each other. For the input operation, the face for input by touching (the face opposite to the face having the transparent conductive thin film) of the plastic substrate of the touching side is pressed by a pen or a finger and the transparent conductive thin film of the plastic substrate of the touching side and the transparent conductive thin film of the display side are brought into contact with each other.
However, the touch panel of the resistance film type has a problem in that the surface of the touching side is damaged and the transparent conductive thin film in the plastic substrate (the substrate material film) of the touching side is worn, has cracks or separated from the substrate after the transparent conductive thin film of the plastic substrate of the touching side and the transparent conductive film of the transparent substrate of the display side are repeatedly brought into contact with each other. To overcome the above problem, it is widely conducted that hard coat layers of a synthetic resin are disposed on the surface of the touching side and between the transparent plastic substrate and the transparent conductive thin film.
A polarizing film in which a film for prevention of reflection is disposed on a hard coat layer containing a resin curable with radiation or the like and ultra-fine particles of titanium oxide treated on the surface with a metal oxide or the like to improve the surface of the touching side is proposed (Japanese Patent Application Laid-Open No. 2000-171603).
Conventional hard coat films having a hard coat layer formed and kept on a substrate film by curing by heating or by irradiating an ionizing radiation exhibit shrinking by curing and shrinking under the condition of a high temperature and a high humidity markedly and tend to cause the curling phenomenon in which end portions of the hard coat films are curled up since the constituting components in the conventional technology are mostly polyfunctional acrylates. Moreover, optical interference fringes are occasionally formed due to the difference in the refractive index between the substrate film and the hard coat layer and a method to overcome the drawback is additionally required. The drawbacks of the conventional hard coat films are the shrinking by curing, the shrinking and curling under the effect of a higher temperature and a high humidity and the optical interference fringes.